1. Field of the Invention
This invention is related to a data replication system including storages and, in particular, to a method for migrating the replication system whereby downtime of applications during the migration and cost of migration are reduced.
2. Description of the Related Art
Storage-Based Replication System
A storage-based replication system is a system that utilizes storage-based replication functions for remote replication and/or in-system replication. The details of remote replication and in-system replication are discussed below.
Remote Replication
Storage-based remote replication is a function in a storage system to replicate data, such as one or more entire volumes, from a production site or a primary site to a remote site or a secondary site while maintaining data integrity. The replicated data is usually called a “replica” or mirror. The technology is used for Disaster Recovery (DR), and the like, in case of failure of the primary storage system. In the event of such a failure, users can recover at least production data from the replicated data at the remote site when the production site happens to be corrupted or inoperative due to a disaster, or the like. Examples of storage-based remote replication systems are Hitachi TrueCopy™, EMC SRDF™, and IBM Peer to Peer Remote Copy (PPRC). Remote replication is also called remote mirroring or remote copy.
In-System Replication
Storage-based in-system replication is a function in a storage system to replicate data or a volume within the storage system. The replicated data will then be backed up to tape or other suitable media to protect against any data loss. Examples of the storage-based in-system replication are Hitachi ShadowImage™, QuickShadow™, EMC TimeFinder, BCV, and IBM FlashCopy™. In this disclosure, “replication” means a function or a system using a replication function, depending on the context of use.
Migrating Replication
It is sometimes necessary for users to migrate their storage system. For example, when a vendor introduces a new storage system, the users may want to update their existing storage system to the new system. In this case, data in the existing storage system needs to be migrated to the new storage system, and applications need to be stopped during the migration. Additionally, if the existing storage system is configured to execute replication, the users will usually want to migrate the replication system as well. Thus, there are at least two issues of concern: first, applications using the existing storage need to be stopped during the migration; and second, migrating replication adds complexity and requires a higher labor cost because the replica and its environment must also be migrated.
With respect to the stoppage of applications, any applications using the storages need to be stopped during the migration so as to prevent data loss and maintain data consistency. However, it is now common for some users to run their business applications continuously (i.e., 24 hours a day, 7 days a week), and their businesses are dependent upon the applications being able to run. Stopping the applications usually results in lost business or productivity. Therefore, these users prefer to reduce or eliminate the time for stopping applications as much as possible so that downtime, lost income, and lost productivity are minimized.
Further, with respect to the second issue, migrating replication requires an additional labor cost and adds complexity to the data migration process. Migrating replication data requires migrating both the replica and its environment, such as replication configuration. Accordingly, the present invention aims to reduce not only cost but also the complexity associated with migrating replication data and configurations.
Virtualization
Recently, virtualization has become a popular technology in the storage industry. The SNIA (Storage Networking Industry Association) defines “virtualization” as “the act of integrating one or more (back end) services or functions with additional (front end) functionality for the purpose of providing useful abstractions. Typically virtualization hides some of the back end complexity, or adds or integrates new functionality with existing back end services. Examples of virtualization are the aggregation of multiple instances of a service into one virtualized service, or to add security to an otherwise insecure service. Virtualization can be nested or applied to multiple layers of a system.” (See, SNIA webpage: http://www.snia.org/education/dictionary/v/) In this disclosure, the term “virtualization” is used to mean a technology, function or system using virtualization technology, and also depends upon the context in which it is used.
A virtualization system is a system incorporating virtualization technology. Examples of virtualization systems are Hitachi USP (Universal Storage Platform) whose virtualization function is called as Universal Volume Manager, IBM SVC (SAN Volume Controller), EMC Invista™ (formerly Storage Router), CISCO MDS, and the like. Also, it should be noted that some virtualization systems themselves, such as Hitachi USP, combine the storage system with virtualization.
Prior art storage systems are exemplified by U.S. Pat. No. 6,098,129 to Fukuzawa et al., and U.S. Published Patent Application No. 20030221077 to Ohno et al., the disclosures of which are incorporated by reference herein in their entireties. Additionally, some products include data migration services, replication implementation services and/or replication management software. Some examples of these products are listed in the following web sites:                http://www.hds.com/products_services/services/productbased/        http://www.hds.com/products_services/services/storage_solution/        http://www.emc.com/global_services/catalog/business_implementation.jsp        
Co-pending U.S. application Ser. No. 10/788,390, filed Mar. 1, 2004, by Akira Fujibayashi, is directed to a method and apparatus for performing data migration in storage systems implementing a remote copy function and virtualizing storage of existing storage devices in a new storage system after migrating the existing storage data to the new storage devices. When a new storage system is connected to an old storage system destined for replacement and prior to starting data migration, remote copy configuration information from the old storage system is migrated to the new storage system. This allows either the new storage system or the old storage system, depending on the configuration, to maintain an operational remote copy function with a remote storage system during the data migration. Thereafter, data is migrated from the old storage system as a virtual volume to the new storage system while data is being transferred between the new storage system and the remote storage system in accordance with the remote copy configuration information. U.S. application Ser. No. 10/788,390 is hereby incorporated by reference in its entirety.